Browsing by Author "Lai, Chun-Han"

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A facile approach to fabricate Ni inverse opals at controlled thickness
(2009-11-15)
Huang, Yi-Jui
;
Lai, Chun-Han
;
Wu, Pu-Wei
;
Chen, Li-Yin
;
材料科學與工程學系
A vertical electrophoretic deposition method was employed to fabricate polystyrene (PS) colloidal crystals with negligible defects and considerable surface uniformity. Subsequently, the interstitial voids within the colloidal crystals were electroplated with Ni, followed by selective removal of the PS microspheres. With careful adjustment in the processing parameters. we were able to obtain Ni inverse opals at predetermined thickness in relatively short time. The inverse opals revealed superb structural stability and surface uniformity. Because the electrophoresis and electrodeposition were both carried out in a solution state, this fabrication scheme enables facile construction of inverse opals on conductive substrates over conventional approaches. (C) 2009 Elsevier B.V. All rights reserved.
Conformal deposition of Ni-P on anodic aluminum oxide template
(2008)
Lin, Sheng-Chieh
;
Lai, Chun-Han
;
Wu, Pu-Wei
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A nanoporous semiconducting template was fabricated by conformal deposition of Ni-P over anodic aluminum oxide (AAO). Electroless plating was conducted in repeated steps of sensitization, activation, and deposition using NaH2PO2 as a reducing agent. Variables including pH, temperature, time, and additive were studied for conformal deposition within the pore channels without clogging the openings prematurely. We demonstrated concentric Ni-P tubes with an inner diameter of 84 nm at 10 mu m length. Resistivity of the AAO template was determined at 39.6 Omega cm for through-channel direction. Incorporation of the semiconducting AAO structure with established template synthesis technologies opens up the opportunity for numerous devices. (C) 2007 The Electrochemical Society.
Effect of Crystallinity on the Optical Reflectance of Cylindrical Colloidal Crystals
(2011)
Lai, Chun-Han
;
Yang, Yu-Lin
;
Chen, Li-Yin
;
Huang, Yi-Jui
;
Chen, Jing-Yu
We fabricate cylindrical colloidal crystals (CCCs) via electrophoretic depositions of polystyrene microspheres on a carbon fiber in a concentric arrangement. Images from optical and scanning electron microscope indicate that the CCCs of 460 nm microspheres reveal a semicrystalline structure in close-packed lattice, while the CCCs of 660 exhibit an amorphous arrangement. In optical reflectance spectra, both CCCs demonstrate a dispersive photonic bandgap as compared to that from planar counterparts. The curved contour for the CCCs renders incident light interacting with reflecting planes at slightly different angles, leading to a notable reduction in the reflectance intensity and minor relocation of photonic bandgap contingent on their crystallinity. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3536511] All rights reserved.
Electrowetting of Superhydrophobic ZnO Inverse Opals
(2011)
Chen, Li-Yin
;
Lai, Chun-Han
;
Wu, Pu-Wei
;
Fan, Shih-Kang
;
材料科學與工程學系
ZnO inverse opals are fabricated by electrophoresis of polystyrene (PS) microspheres (720 nm in diameter) on a ITO glass to form a close-packed colloidal crystal, followed by potentiostatic deposition of ZnO in the interstitial voids among the PS microspheres and chemical removal of the PS colloidal template. By adjusting the electrodeposition time, we obtain semi-layered and multi-layered ZnO inverse structures with significantly reduced defects and considerable surface uniformity. The semi-layered ZnO inverse opals display a bowl-like morphology with individual cavities isolated from each other. In contrast, the multi-layered ZnO inverse opals exhibit a three-dimensional skeleton with hexagonally-arranged cavities interconnected to each other. After surface coating of perfluorodecyltriethoxysilane, both samples reveal a superhydrophobic nature with contact angle larger than 150 degrees. In electrowetting measurements, the contact angles are decreasing with increasing applied voltages. The droplet on the semi-layered ZnO inverse opals demonstrates a notable transition from the Cassie-Baxter state to the Wenzel one. However, the droplet on the multi-layered ZnO inverse opals indicates three distinct regimes; Cassie-Baxter state, mixed Cassie-Baxter/Wenzel state, and Wenzel state. Repelling pressure of the entrapped air in the cavities is estimated to explain the observed contact angle variation upon the applied voltage for both samples. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3594723] All rights reserved.
Enhancement of bifunctional catalysis by Ir doping of La0.6Ca0.4CoO3 perovskites
(2008-10-15)
Chang, Yun-Min
;
Hsieh, Yu-Chi
;
Wu, Pu-Wei
;
Lai, Chun-Han
;
Chang, Tin-Yu
La0.6Ca0.4Co0.8Ir0.2O3 was prepared by solid state reaction synthesis from mixtures of La(NO3)(3)center dot 6H(2)O, Ca (NO3)(2)center dot 4H(2)O, Co(NO3)(3)center dot 6H(2)O, and IrO2 at stoichiometric ratio. Images from scanning electron microscopy on the as-synthesized powders exhibited particles in irregular shape at 100-250 nm in size. X-ray diffraction analysis confirmed the formation of perovskite without the rutile signals from IrO2, suggesting successful incorporation of Ir4+ at the Co cation sites. The carbon nanocapsules (CNCs) were used as an electrocatalyst support. Electrodes for electrochemical measurements were fabricated by depositing mixtures of CNCs, La0.6Ca0.4Co0.8Ir0.2O3 and polymeric binders on commercially available noncatalyzed gas diffusion electrodes. In alkaline electrolyte, the La0.6Ca0.4Co0.8Ir0.2O3/CNCs demonstrated superior performances than those of La0.6Ca0.4Co0.8Ir0.2O3/CNCs and IrO2/CNCs in both charging and discharging current-potential polarization measurements. (c) 2008 Elsevier B.V. All rights reserved.
Fabrication of Large-Area Colloidal Crystals by Electrophoretic Deposition in Vertical Arrangement
(2008)
Huang, Yi-Jui
;
Lai, Chun-Han
;
Wu, Pu-Wei
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Fabrication of large-area colloidal crystals (400 mu m(2)) with superb uniformity in multiple layers (similar to 128 layers) from SiO(2) microspheres (similar to 400 nm) was achieved by electrophoresis in vertical arrangement. With a large difference in electrode areas and selection of ethanol as the solvent, we investigated self-assembly with SiO(2) suspensions at various pH and electric fields of 20-100 V cm(-1). Colloid formations with negligible vacancies and small-angle grain boundaries were obtained at a suspension of pH approximate to 10 and electric field of 20 V cm(-1). Our fabrication scheme enables construction of colloidal crystals with significantly reduced structural disorders as compared to conventional routes. (C) 2008 The Electrochemical Society.
Ni Inverse Opals for Water Electrolysis in an Alkaline Electrolyte
(2010)
Huang, Yi-Jui
;
Lai, Chun-Han
;
Wu, Pu-Wei
;
Chen, Li-Yin
;
材料科學與工程學系
A vertical electrophoretic deposition technique was employed to prepare polystyrene (PS) colloidal crystals with negligible crystallographic defects. The colloidal crystals were plated with Ni, followed by selective removal of PS microspheres to fabricate inverse opals. With adjustments in relevant processing parameters, we were able to obtain inverse opals in multiple layers with excellent surface uniformities. The inverse opals were used as the electrode material for water electrolysis. Results from current-potential polarizations in 1 M KOH aqueous solution indicated that the catalytic abilities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) increased with the layers of inverse opals. Estimation of the effective current densities determined that the entire area of the inverse opals was available for electrochemical reactions. In galvanostatic measurements for both OER and HER, the inverse opals demonstrated stable voltage profiles without notable degradations for 120 h. Compared with a planar Ni plate, the inverse opals exhibited a significantly reduced overpotential for the water electrolysis.
Physical Characterizations of Ni-Plated Carbon Fibers after Controlled Thermal Treatments
(2009-03-01)
Lai, Chun-Han
;
Liu, Guan-Ting
;
Wu, Pu-Wei
;
Chiu, Yu-Fan
;
Chou, Chao-Ling
Surface modifications of carbon fibers (CFs) were conducted by electroless Ni depositions. After annealing in air at 300 degrees C, we fabricated a composite in NiO/Ni/CFs configuration. The samples revealed reasonable surface uniformities without defects at the interfaces. Values for the electrical resistivity indicated a steady increase with annealing time, reaching a plateau after 72h. Results on the tensile stress exhibited a marked reduction once the NiO was formed. A thermal treatment at 700 degrees C for 48 h in air allowed complete removal of the CFs, forming NiO hollow tubes with an inner diameter of 6.50 mu m. Subsequently, they were transformed into Ni hollow tubes with a reduced inner diameter of 5.53 mu m under a hydrogen treatment at 400 degrees C for 3 h. The NiO and Ni tubes demonstrated impressive structural integrities with considerable mechanical strengths. (C) 2009 The Japan Society of Applied Physics
Rapid Fabrication of Cylindrical Colloidal Crystals and Their Inverse Opals
(2010)
Lai, Chun-Han
;
Huang, Yi-Jui
;
Wu, Pu-Wei
;
Chen, Li-Yin
;
材料科學與工程學系
We employed an electrophoretic deposition technique to prepare cylindrical colloidal crystals (CCCs) from polystyrene (PS) microspheres of 460 and 660 nm diameters using a carbon fiber (CF) with 7 mu m diameter as the substrate. Measurements on the CCC diameter demonstrated growth rates that slowed down as time progressed. Scanning electron microscope images confirmed that the CCCs of 460 nm microspheres formed a face-centered cubic close-packed lattice, whereas an amorphous structure appeared for the CCCs of 660 nm. Subsequently, both CCCs underwent a potentiostatic electroplating to deposit Ni into the interstitial voids among the PS microspheres. After chemical removal of the PS microspheres, we fabricated cylindrical inverse opals (CIOs) in various diameters. As expected, better crystallinity was found on the CIOs of 460 nm microspheres as opposed to the 660 nm ones. The electrical resistivity for both CIOs exhibited a substantial reduction over that of the CF. Our CCCs and CIOs revealed considerable structure stability with excellent surface uniformity. The fabrication scheme enables rapid preparations of CCCs and CIOs in desirable lengths and diameters.